LAUSR

Purpose The purpose of this study was to use the finite element method (FEM) to reproduce fracture lines that reach the lateral tibial plateau during open-wedge high tibial osteotomy (OWHTO) in patients with Type III lateral hinge fracture (LHF). It was hypothesized that the FEM could clarify biomechanical causes of Type III LHF, enabling prevention of adverse complications. Methods This study used the nonlinear FEM to analyze the data of eight knees in eight patients (two males and six females) with Type III LHF among 82 patients who underwent OWHTO, as well as the data of eight individuals with no LHF. To predict the onset of Type III LHF, simulation models were also developed in which posterior osteotomy sufficiency varied from 50% to perfect, the latter defined as osteotomy reaching the hinge point. Results Real-life instances of Type III LHF caused by insufficient posterior osteotomy were reproduced in all patient-specific FEM models, and these models accurately predicted fracture types and locations. During opening of the osteotomy gap, the fracture line reached the lateral tibial plateau, and extended vertically from the end of the insufficient posterior osteotomy, avoiding the rigid proximal tibiofibular joint. In contrast, sufficient posterior osteotomy resulted in a lack of LHF. Posterior osteotomy extension ≥ 70% of the width of the osteotomy plane was the cut-off value to prevent Type III LHF. Conclusion Forced opening of insufficient posterior osteotomy was found to be a biomechanical cause of Type III LHF that extended perpendicularly to the lateral tibial plateau, avoiding the proximal tibiofibular joint. The clinical significance of this study is that sufficient posterior osteotomy during OWHTO, defined as at least 70% of the width of the osteotomy plane, can prevent Type III LHF.